The invention relates to improvements in methods of and apparatus for treating waste oil and other long-chain compounds of high molecular weight including pyrolysis oil (hereinafter referred to only as waste oil). More particularly, the invention relates to improvements in methods of and apparatus for treating waste oil wherein waste oil is treated in a continuous operation including heating, fractionating and distilling to obtain a variety of products of different qualities and compositions. Still more particularly, the invention relates to improvements in methods of and apparatus for treating waste oil in such a way that the treated material yields a plurality of side stream fractions and that the path for the flow of waste oil during treatment is kept free of deposits, such as coke and others.
Heretofore known treatments of waste oil involve multistage distilling operations including conveying of waste oil through heated tubes and heating of waste oil in other types of heat exchanger means to a temperature of approximately 300.degree. C. prior to processing of heated waste oil in large-capacity reaction columns. The arrangement is or can be such that a first stage involves a treatment at atmospheric pressure, and a following second stage involves a treatment below atmospheric pressure. The residues can be removed by distillation in a third stage at less than atmospheric pressure. One of the just outlined methods is known as sulfuric acid-bleaching earth process. A drawback of such methods is that the period of dwell of waste oil in the apparatus is very long. Moreover, and since the receptacles for waste oil are very large, it is difficult to control the temperature and the pressure with a requisite degree of accuracy. As a rule, pressures to which waste oil is subjected in such apparatus cannot be reduced to less than approximately 60-100 mbar. Therefore, it is often necessary to operate at very high temperatures, depending on the boiling points and evaporation temperatures of certain fractions. In many instances, the temperatures are only slightly below the cracking temperature of waste oil. On the other hand, cracking of the treated compound must be avoided in order to ensure that such compound will retain its satisfactory lubricating characteristics.
Another drawback of conventional methods and apparatus is that they yield large quantities of acid tar and bleaching earth which is undesirable for ecological reasons. The cost of waste disposal is quite high because the yield normally does not exceed 60% and approximately 20% of treated compound consists of acid tar which must e disposed of at a substantial cost. The remaining 20% of the admitted material is removed in the form of water vapors.
In order to avoid the drawbacks of the above outlined conventional methods and apparatus, certain more recent proposals involve the utilization of thin film evaporators. Attempts to further develop such treatment of waste oil involve the utilization of super critical gases. However, this entails a huge initial and maintenance cost. Moreover, and since such methods are designed for the treatment of rather large volumes of waste gas under circumstances when the treated material is readily ignitable, the danger of explosion and fire is ever present. This, in turn, involves additional outlays for the reasons of safety. Furthermore, the apparatus for the practice of such method must be designed to stand elevated pressures of up to 150 bars.